1. Field of the Invention
The present invention generally relates to annotating data objects and, more particularly, to determining the validity of annotations by detecting changes in the annotated data.
2. Description of the Related Art
An annotation system is one where descriptive information is stored about objects, or parts of objects. Some annotation systems store annotations separately, without modifying the objects themselves. An annotation store, typically a database, contains information for the annotation, typically in the form of descriptive text, or other classifiers. An indexing scheme is typically used to map each annotation to the object or positions of annotated portions within the object. The annotation system may be configured to display the annotation in response to the user selecting the annotated portions of the object. For example, one common method for displaying annotations is in a flyover text box generated when a user positions a mouse pointer in proximity to the annotated portion or portions of the object.
The annotations themselves may serve different functions for different applications. For example, for some applications, annotations may serve as an interactive help system, providing description of the functionality, or explain the use of the annotated object. As an example, in a business application, an annotation may explain the use of an economic performance parameter, such as a current year's revenue by division. For other applications, annotations may serve to provide expert feedback, comments, or clarifications from a reviewer or a creator of a document or other data object. As examples, the creator of a document may insert an annotation highlighting the relevance of a certain piece or group of data, while a reviewer of the same document may insert an annotation with instructions for revising the document, possibly to correct an error.
In many instances, however, the annotation system and an application used to create or modify the annotated object may act independently. Thus, the annotated object may change without the permission, or foreknowledge of the annotation system. As a result, annotations that were valid prior to a change may no longer be valid after the change. Using the example above, the creator of the document may correct an error as suggested in the reviewer's annotation without updating (or deleting) the annotation. Thus, the annotation invalidly refers to an error that has already been corrected, which may mislead a future viewer of the annotation.
Conventional methods for detecting changes to a data object typically involve calculating a checksum for the data object. In general, a checksum is a numerical value generated by an algorithm performed on each bit in the data object. The algorithm is designed so that a change to even a single bit in the data object results in a new checksum. Thus a change in the data object may be detected by comparing checksums generated for the data object at different points in time. A mismatch in the checksum indicates a change occurred somewhere in the data object.
However, an annotation typically only refers to a portion or set of portions of the object. Accordingly, it is possible for annotations referring to parts of an object that have not changed to remain valid, even when other parts of the data object have changed. As an example, in an array or matrix of data (such as a spreadsheet), an annotation may be made for a cell, a row, a column, a group of columns, or any discontinuous group of data points. A change to other data in the array (not referenced by the annotation) would not invalidate the annotation. As another example, in a text document where annotations are made on a paragraph, a change to another paragraph later in the document (or addition of a paragraph) would not change the validity of the annotation on the earlier paragraph. Because conventional methods for detecting a change to a data object typically generate a checksum for the entire data object, a mismatch in checksums indicates a change in the data object as a whole, but not what portion was changed.
Therefore, conventional checksum methods applied to an entire data object are too general and thus inadequate for determining the validity of an annotation referring to a specific portion of the data object. Accordingly, a method is needed to validate an annotation referring to a specific portion of a data object by detecting whether the specific annotated portion has changed since the annotation was created.